The human ear may be divided into the following areas: outer ear (auricle), middle ear, and inner ear. The middle ear comprises the eardrum and the auditory ossicles hammer, anvil, and stirrup. The eardrum is caused to oscillate via sound waves entering the outer ear. These oscillations may be transmitted via hammer, anvil, and stirrup to the oval window of the inner ear, by which sound oscillations may in turn be generated in the liquid of the cochlea. The hair cells projecting into the cochlea are bent by the movement of the liquid and thus trigger nerve pulses. A mechanical impedance conversion occurs in the middle ear, which allows an optimum transmission of the sound signal from the outer ear to the inner ear.
In addition, the tympanic muscle and the so-called stapedius muscle are located in the middle ear. The tympanic muscle is linked to the hammer, the stapedius muscle being connected via a tendon to the stirrup. In case of an excessively high sound pressure, which could damage the inner ear, both muscles contract reflexively, so that the mechanical coupling of the eardrum to the inner ear (and thus also the force transmission) is decreased. In this way, it is possible to protect the inner ear from excessively high sound pressures. The tensing of the stapedius muscle triggered as a result of high sound pressures is also referred to as the stapedius reflex. Medically relevant information about the functional capability of the ear may be obtained from the diagnosis of the stapedius reflex. Furthermore, the measurement of the stapedius reflex is useful for setting and/or calibrating so-called cochlear implants, because the sound energy perceived by a patient may be concluded from the measured stapedius reflex.
Using electrodes, which are brought into contact with the stapedius muscle and which relay action current and/or action potentials generated upon a contraction of the stapedius muscle to a measuring device, is known for measuring the stapedius reflex. A reliable, minimally-invasive contact of the stapedius muscle is difficult, because the stapedius muscle is situated inside a trough present in a bone and only the tendon of the stapedius muscle connected to the stirrup and its upper part are accessible from the interior of the middle ear.
Various stapedius muscle electrodes are known from U.S. Pat. No. 6,208,882. However, these only achieve inadequate contact of the stapedius muscle tissue (in particular upon muscle contraction) and are also very traumatizing.
DE 10 2007 026 645 A1 discloses a two-part bipolar electrode configuration where a first electrode is pushed onto the tendon of the stapedius muscle or onto the stapedius muscle itself, and a second electrode is pierced through the first electrode into the stapedius muscle. One disadvantage of the described solution is its rather complicated handling in the very limited space of a surgical operation area. In addition, the piercing depth of the second electrode is not controlled so that trauma can also occur with this approach.
It would be advantageous to have a simple cost effective electrode for measuring action currents and/or action potentials in electrically active tissues (such as the stapedius muscle tissue), which enables secure but reversible fixing of the electrode in the target tissue, but which traumatizes the tissue as little as possible.